Downhole circulation tools have been used for decades to selectively flow fluid from the interior of a tubing string or work string to the annulus surrounding the tool. Some tools have the ability to selectively close off circulation ports to subsequently pass fluid down the tubing string or work string. Many of these tools, however, make it difficult or unreliable to pass a cementing plug through the work string after the circulation ports are closed without damaging the plug. Other tools require that the work string be placed on bottom or engage some type of restriction in the well to cycle the tool. Various types of circulation tools have thus been devised for circulating fluid within a tubular string to an annulus, and for subsequently moving a sleeve to close the annulus so that fluid can be passed through the tool.
Prior art circulation tools for selectively closing off flow through a side port in the tool and for subsequently passing cement and cement plugs through the tool include tools with a deformable or expandable seat to allow the ball to pass through the seat and thus through the tool once the sleeve has shifted to close off flow ports in the tool. This type of tool significantly restricts the size of the cement plug which may be reliably passed through the tool, and the deformable seats may damage the plug wiper seals or rubber wafers while passing through the deformable seat. As a consequence, cementing operations are adversely affected since an unknown quantity of cement may pass by the wiper plug after the wiper plug has passed through the tool. Other types of tools employ a flangible disc within the bore of the tool. Pressure builds up on top of the disc to shift a sleeve to close off the circulation ports. A subsequent increase in pressure breaks the flangible disc. Fragments from the disc can be very damaging, however, to a cementing plug which is subsequently passed through the tool. Disc fragments may cut or tear at the wiper plug, thereby damaging the wiper plug.
Another type of tool utilizes a J-type mechanism for moving the sleeve between the open and closed positions. This type of tool or a tubular extending downward from the tool conventionally sits on the bottom of the well so that weight can be applied to manipulate the J-type mechanism.
Other types of surge tools do not provide substantially a full bore opening through the tool, and the restriction in the ID of the tool is thus a significant detriment to the use of the tool.
U.S. Pat. No. 6,275,929 discloses a circulation tool with axially moveable sleeves. Similar tools are disclosed in U.S. Pat. Nos. 6,571,875 and 5,176,208. U.S. Pat. No. 5,402,850 discloses a tool for reverse circulation of fluid in the wellbore. A circulation tool with wash ports is disclosed in U.S. Pat. No. 4,987,841. Another type of circulation tool is disclosed in U.S. Pat. No. 4,657,092. A downhole tool with a combination ball valve and sliding sleeve is disclosed in U.S. Pat. No. 5,335,731.
The disadvantages of the prior art are overcome by the present invention. An improved downhole circulation tool which may be reliably used with cementing operations is subsequently disclosed.